The present invention relates generally to the field of implantable medical devices. More particularly, the invention relates to a sensing device and method for determining aneurismal pressure in a body cavity.
Vascular aneurysms are produced when a thinning or weak spot in a vessel wall dilates eventually posing a health risk from its"" potential to rupture, clot, or dissect. While aneurysms can occur in any blood vessel, most occur in the aorta and peripheral arteries. The majority of aortic aneurysms occur in the abdominal aorta, usually beginning below the renal arteries and often extending into one or both of the iliac arteries. The etiology of aneurysm formation is not entirely understood, but is thought to be related to congenital thinning of the artery, atherosclerotic vessel degeneration, vessel trauma, infection, smoking, high blood pressure, and other causes leading to vessel degeneration. Left untreated, aneurysms may lead to gradual vessel expansion, thrombus formation leading to stroke or other vessel blockage, vessel rupture, shock, and eventual death.
Aneurysms may be treated in open surgical procedures, where the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While considered to be an effective surgical technique, particularly considering the alternative of the usually fatal ruptured aneurysm, conventional vascular graft surgery suffers from a number of disadvantages. The surgical procedure is complex and requires experienced surgeons and well equipped surgical facilities. Even with the best surgeons and equipment, patients suffering from such aneurysms are often elderly and weakened from cardiovascular and other diseases. This factor reduces the number of patients eligible for surgery. Even for eligible patients prior to rupture, conventional aneurysm repair has a relatively high mortality rate, usually from 2 to 10%. Morbidity related to the conventional surgery includes myocardial infarction, renal failure, impotence, paralysis, and other conditions. Even with successful surgery, recovery takes several weeks and often requires a lengthy hospital stay.
To overcome some of the drawbacks associated with open surgery, a variety of endovascular prosthesis placement techniques have been proposed. Without the need for open surgery, patient complications and recovery time may be significantly reduced. The most common type of aneurysm, the abdominal aortic aneurysm (AAA) may be used as an example for treatment with a prosthetic device. For example, one endovascular AAA repair technique involves a tubular prosthesis deployed by remote insertion through a femoral artery. A stent-graft prosthesis permits a sealed shunt of blood flow from a healthy portion of the aorta, through the aneurysm, and into one or both of the iliac artery branches. The prosthesis excludes any thrombus present in the aneurysm while providing mechanical reinforcement of the weakened vessel reducing the risk of dissection and rupture, respectively. Furthermore, the prosthesis can substantially reduce the blood pressure within the isolated aneurysmal sac providing the weakened vessel with a favorable healing environment. Backflow from blood vessels in communication with the aneurismal sac may continue to pressurize the, aneurysm despite the presence of a shut.
A known shortcoming of some of the implantable endovascular prosthetics relates to migration and seal. The affected vessel(s) may vary widely in location, size, and the distended shape of the aneurysm itself. Particularly after treatment, the aneurysm and associated vessels may drastically change morphology thereby exerting stress forces on the deployed prosthesis. With sufficient change in aneurysm morphology and subsequent stress placed on the prosthesis, the device may migrate and/or detach from the vessel wall. As a result, the fluid seal may be compromised and blood may leak into the aneurysm from the aorta thereby elevating the aneurysmal pressure. The patient may have to undergo another treatment given the problem is detected early. The described or other undetected xe2x80x9cendoleakagexe2x80x9d may lead to aneurysm growth or regrowth, and to the more serious problems associated with aneurysms. Accordingly, it would be desirable to provide a strategy for monitoring an aneurysm.
Current strategies for monitoring aneurysms involve imaging by means of CT-scan magnetic resonance, angiography, duplex ultrasound, and the like. These imaging methods may utilize a contrast solution to enhance the visualization process. Some patients may be allergic to the iodine based solutions and other xe2x80x9cdyesxe2x80x9d. In certain situations, the patient may experience a warm xe2x80x9cflushedxe2x80x9d sensation, a transient metallic taste, or a mild itching over various parts of the body with developing hives. In rare situations, the patient may suffer from a strong, sudden, and systemic response to the contrast solutions. Such anaphylactic responses may involve mental confusion, dizziness (due to a drop in blood pressure), swelling (especially of the face, tongue and throat), and difficulty breathing. The reactions can be more serious if not treated immediately. Therefore, it would be desirable to provide a strategy for monitoring an aneurysm without the use of appreciable volumes of contrast solution.
Another shortcoming of the aforementioned imaging strategies relates to sensitivity. Current methods may effectively visualize the size and shape of the aneurysm, providing a passive monitoring strategy. However, such methods may not effectively detect the presence of an endoleak. For example, the aneurysm may be largely filled with a thrombus. A sufficient amount of contrast solution may not be introduced into the aneurysm. This circumstance may lead to a reduced capacity in detecting endoleakage. Continued undetected endoleakage, even at a low level, may slow or even reverse the aneurysmal healing process. To avoid this and other situations where endoleakage cannot be detected, it may be more advantageous to measure endoleaks more directly. As such, it would be desirable to provide a strategy for directly measuring aneurysmal pressure.
Therefore, it would be desirable to provide a sensing device and method for determining aneurismal pressure that overcomes the aforementioned and other disadvantages.
One aspect according to the invention provides a device for sensing aneurysmal pressure in a body cavity. The device includes a housing including at least one chamber formed therein. A first fluid is positioned in a first portion of the chamber. A second fluid is positioned in a second portion of the chamber. A compressible fluid is positioned in the second portion of the chamber. A divider is positioned between the first and second fluids. A pressure membrane is in communication with the first portion of the chamber. The aneurysmal pressure is transmitted through the membrane and the first fluid to position the divider within the chamber. The body cavity may be an aorta. The first and second fluids may be non-miscible. At least one of the first and second fluids may include a biocompatible hydrocarbon and/or a radiopaque fluid. The radiopaque fluid may include barium sulfate, diatrizoate, iodipamide, iohexol, iopamidol, iothalamate, ioversol, ioxaglate, and metrizamide. The divider may be manufactured from a radiopaque material such as gold, silver, tantalum oxide, tantalum, platinum, platinum/iridium alloy, and tungsten. An anchor portion may be operably attached to the housing, wherein the anchor retains the housing adjacent the aneurysm. At least one gas may be positioned in the chamber, wherein the gas volume changes in response to the aneurysmal pressure. At least one radiopaque marker may be disposed on the housing. An endoluminal prosthesis may be positioned adjacent the aneurysm. A divider membrane may be positioned adjacent the compressible fluid and the second fluid, wherein the second fluid may be a liquid.
Another aspect according to the invention provides a method for determining aneurysmal pressure in a body cavity. The method includes deploying a sensing device including radiopaque substance adjacent an aneurysm. The radiopaque substance is moved within the device in response to the aneurysmal pressure. The sensing device is imaged. The body cavity may be an aorta. The sensing device may be deployed with a catheter. The sensing device may be retained adjacent the aneurysm. The sensing device may be imaged fluoroscopically. The sensing device may be calibrated. Calibration may include adjusting a radiopaque substance position with respect to a standard pressure and/or adjusting a rate of radiopaque substance movement with respect to the aneurysmal pressure before deployment. An endoluminal prosthesis may be deployed adjacent the aneurysm.